1. Field of the Invention
The present invention relates generally to network communications and diagnostics, and more specifically, to network communications and diagnostics wherein a network communications medium is tested for faults that may affect the ability of the medium to transmit data between the network devices connected to it. Particular utility for the present invention is found in the area of computer networks utilizing Digital Subscriber Line (DSL) modem-based connections, although other utilities are also contemplated for the present invention, including other communications and computer networking applications.
2. Brief Description of Related Prior Art
A Modulator-Demodulator (xe2x80x9cmodemxe2x80x9d) is a communication device that permits communications between networked devices. More specifically, a modem (1) encodes, transforms, and organizes (xe2x80x9cmodulatesxe2x80x9d) digital data supplied from a sending digital device (e.g., one or more digital computer systems) into a form suitable for transmission (e.g., frames of analog signals from which the data may be recovered and which includes appropriate frame checksums and other information) over a network communications medium (e.g., lines of a public switched telephone network, cable system, or other type of communications link), (2) transmits the frames via the medium, and (3) receives and transforms (xe2x80x9cdemodulatesxe2x80x9d) modulated frames (i.e., sent from another modem) so as to recover from the received frames the original digital data from which the received frames were generated, which recovered digital data is provided for further processing to a receiving digital device. Additionally, modems typically also perform a variety of communications control functions (e.g., initiating and coordinating the data exchange, negotiating data transfer rate with the other modem involved in the data transfer, etc.).
Many different types of modems are available, and the characteristics of modems vary depending upon their data transmission rates, modes of use (e.g., for serial or parallel transmission, synchronous or asynchronous transmission, simplex, duplex, or full-duplex operation, etc.), modulation/demodulation/compression techniques, error correction technologies, nature of their modulated signals (e.g., digital or analog), etc. Additionally, some conventional modems (e.g., modems which utilize certain Rate Adaptive Digital Subscriber Line (RADSL) technology, such as Discrete Multi-Tone (DMT) technology) include hardware and software for determining the quality of the medium (i.e., ability of the medium to support modulated data transmissions between the sending and receiving modems, without exceeding a predetermined data exchange error rate threshold, in given communications channels and/or at given transmission rates). Based upon the quality of the data exchange medium, these RADSL modems negotiate their modulated data transmission bandwidth(s) and/or specific communications signal band(s)/channel(s) so as to minimize loss/corruption of data transmitted between the devices.
More specifically, one conventional technique used by certain RADSL modems to adjust their data exchange channel(s) and/or transmission rate(s) based upon the quality of the connection medium, consists of exchanging between the two modems via the medium, predetermined patterns of modulated test data signals at different transmission rates and/or in different signal band(s), determining the respective error rates of such transmissions, determining therefrom the best channel(s) and transmission rate(s) for data exchange that can be supported by the medium connecting the RADSL modems (i.e., the channel(s) that can reliably (i.e., without exceeding the predetermined error rate threshold) support the highest transmission rate(s)), and negotiating based upon these best channel(s) and rate(s) the data communications transmission rate(s) and channel(s) that will be used by the modems in the current session.
Thus, conventional modems can determine if a network communications medium is unable to support reliable data communications at the modems"" maximum communications rates. It would be desirable, however, to provide a modem that is able to determine the nature and location of specific fault conditions in the medium that may be responsible for the medium""s reduced data transmission quality. That is, it would be desirable to provide a modem that includes integrated capability both to classify and locate the whereabouts in the medium of specific physical characteristics/phenomena that may be responsible for reducing the medium""s data transmission quality. Disadvantageously, without such modem capability in order to determine whether reduced transmission quality can be ameliorated (e.g., by physical repair of the medium), human operator intervention is required to determine the nature and location of the specific fault conditions (if any) in the medium that result in the medium""s reduced transmission quality. Typically, such intervention involves time consuming visual inspection and/or testing of the medium using complex and expensive standalone test equipment.
In accordance with one aspect of the present invention, a communication device is provided that includes integrated diagnostic capabilities that permit the device to determine whether a fault condition exists in a communications network to which it is connected. The device includes a processor for generating a diagnostic testing pulse signal that is supplied to the network via the network communications medium to cause the medium to generate a reflection signal from the diagnostic signal. The reflection signal is indicative of whether a fault condition exists in the medium, and may be used by the device to determine the location of the fault condition in the network.
In one preferred embodiment of the invention, the testing signal is a time-domain reflectometry (TDR) stimulus pulse, and the reflection signal is a TDR reflection signal. In this embodiment, the device may use conventional TDR techniques to determine from characteristics of the testing and reflection signals, and the elapsed time from issuance of the testing signal to receipt by the device of the reflection signal, the location of fault conditions (if any) in the network. Such fault conditions may comprise, for example, an impedance discontinuity in the network communications medium. The device of this embodiment may also determine the possible classification of detected fault conditions.
Advantageously, the communications device of the present invention may quickly and efficiently determine the nature and location of specific fault conditions that may be present in the network communications medium. This fault information may be used, either alone or in combination with other diagnostics, to evaluate the medium""s data transmission quality (and/or transmission quality at specific locations therein) to determine appropriate action needed to maintain reliable communications over the network.
These and other features and advantages of the present invention will become apparent as the following Detailed Description proceeds and upon reference to the Figures of the drawings, wherein like numerals depict like parts and in which: